Querydsl4RepositorySupport.applyPagination의 countQuery질문

package kr.co.ibksb.wemeet.api.repository.post;

import kr.co.ibksb.wemeet.api.entity.post.Post;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.stereotype.Repository;

import static kr.co.ibksb.wemeet.api.entity.post.QPost.post;

@Repository
public class PostTestRepository extends Querydsl5RepositorySupport {
	public PostTestRepository() {
		super(Post.class);
	}

	public Page<Post> applyPagination(Pageable pageable) {
		return applyPagination(pageable, contentQuery -> contentQuery
				.selectFrom(post),
				countQuery -> countQuery.select(post.count()).from(post)
		);
	}
}

package kr.co.ibksb.wemeet.api.repository.post;

import com.querydsl.core.types.EntityPath;
import com.querydsl.core.types.Expression;
import com.querydsl.core.types.dsl.PathBuilder;
import com.querydsl.jpa.impl.JPAQuery;
import com.querydsl.jpa.impl.JPAQueryFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.repository.support.JpaEntityInformation;
import org.springframework.data.jpa.repository.support.JpaEntityInformationSupport;
import org.springframework.data.jpa.repository.support.Querydsl;
import org.springframework.data.querydsl.SimpleEntityPathResolver;
import org.springframework.data.support.PageableExecutionUtils;
import org.springframework.stereotype.Repository;

import javax.annotation.PostConstruct;
import javax.persistence.EntityManager;
import java.util.List;
import java.util.function.Function;

@Repository
public class Querydsl5RepositorySupport {

	private final Class domainClass;
	private Querydsl querydsl;
	private EntityManager entityManager;
	private JPAQueryFactory queryFactory;

	public Querydsl5RepositorySupport(Class<?> domainClass) {
		this.domainClass = domainClass;
	}

	@Autowired
	public void setEntityManager(EntityManager entityManager) {
		JpaEntityInformation entityInformation = JpaEntityInformationSupport
				.getEntityInformation(domainClass, entityManager);
		SimpleEntityPathResolver resolver = SimpleEntityPathResolver.INSTANCE;
		EntityPath path = resolver.createPath(entityInformation.getJavaType());
		this.entityManager = entityManager;
		this.querydsl = new Querydsl(entityManager, new PathBuilder<>(path.getType(), path.getMetadata()));
		this.queryFactory = new JPAQueryFactory(entityManager);
	}

	@PostConstruct
	public void validate(){

	}

	protected JPAQueryFactory getQueryFactory() {
		return queryFactory;
	}

	protected Querydsl getQuerydsl() {
		return querydsl;
	}

	protected EntityManager getEntityManager() {
		return entityManager;
	}

	protected <T> JPAQuery<T> select(Expression<T> expr) {
		return getQueryFactory().select(expr);
	}

	protected <T> JPAQuery<T> selectFrom(EntityPath<T> from) {
		return getQueryFactory().selectFrom(from);
	} 

	protected <T> Page<T> applyPagination(
			Pageable pageable,
			Function<JPAQueryFactory, JPAQuery> contentQuery) {
		JPAQuery jpaQuery = contentQuery.apply(getQueryFactory());
		List<T> content = getQuerydsl().applyPagination(pageable, jpaQuery).fetch();
		return PageableExecutionUtils.getPage(content, pageable, jpaQuery::fetchCount);
	}

	protected <T> Page<T> applyPagination(
			Pageable pageable,
			Function<JPAQueryFactory, JPAQuery> contentQuery, Function<JPAQueryFactory, JPAQuery<Long>> countQuery) {
		JPAQuery jpaQuery = contentQuery.apply(getQueryFactory());
		List<T> content = getQuerydsl().applyPagination(pageable, jpaQuery).fetch();
		JPAQuery<Long> countResult = countQuery.apply(getQueryFactory());
		return PageableExecutionUtils.getPage(content, pageable, countResult::fetchOne);
	}
}

안녕하세요. 이동현님, 공식 서포터즈 y2gcoder입니다.

혹시 Querydsl 강의자료를 다시 받아보실 수 있을까요?

받아보시면 영한님께서 pdf 기준 80쪽부터 스프링 부트 2.6 이상, Querydsl 5.0 지원 방법에 대한 안내를 추가해놓으셨습니다. 
말씀하시는 부분도 83쪽부터 설명이 나오니 참고해보시면 좋을 것 같습니다~

감사합니다.